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Why is booleanp defined this way?

From: Marcin Borkowski
Subject: Why is booleanp defined this way?
Date: Fri, 17 Apr 2015 22:34:45 +0200

Hi all,

this is what I found in subr.el:

| (defun booleanp (object)
|   "Return t if OBJECT is one of the two canonical boolean values: t or nil.
| Otherwise, return nil."
|   (and (memq object '(nil t)) t))

Seemingly, it doesn't make much sense: what is the purpose of saying

(and (whatever) t)

instead of just


for a predicate?  Of course, this "normalizes" any "truthy" value to
"t", but is it really needed for anything (except perhaps being


Marcin Borkowski
Faculty of Mathematics and Computer Science
Adam Mickiewicz University

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